The polarization sensitivities of demodulation techniques for tilted fiber Bragg Grating (TFBG) refractometer are investigated theoretically with the complex mode based coupled mode theory. The use of perfectly matched layer (PML) technique simplifies the radiation mode model. The numerical results show that both the normalized area detecting technique and the power-referenced demodulation technique are highly polarization sensitive, the polarization sensitivity increases with the grating tilted angle, thus, precise polarization control is essential in both of the demodulation techniques.